This invention relates to a unique protective device for and a method of protecting surgically implantable, flexible prosthetic joints from laceration or tearing caused by contact with the edges of adjacent bones and which serves to protect the bone from fracture.
Heretofore, various surgically implantable prosthetic devices have been proposed for replacing bone joints. Typically, the prosthesis includes a midsection or hinge portion and a pair of outwardly directed stem portions. The stem portions correspond generally to the dimensions of the intramedullary canals of the bones adjacent the joint and are implanted within the canals. Examples of such prosthetic joints may be found in Applicant's prior U.S. Pat. No. 3,875,594, issued Apr. 8, 1975, and entitled SURGICALLY IMPLANTABLE PROSTHETIC JOINT HAVING LOAD DISTRIBUTING FLEXIBLE HINGE.
As discussed in Applicant's co-pending application Ser. No. 731,825, filed Oct. 12, 1976, and entitled PROTECTIVE SLEEVE FOR IMPLANTABLE PROSTHESIS AND METHOD OF PROTECTING THE PROSTHESIS, experience in testing programs has indicated that the flex life of the flexible implants under consideration is essentially infinite unless a laceration or tear occurs on the surface. The joints are fabricated from flexible elastomeric, physiologically inert material such as silicone rubber. If a laceration or tear of the surface of the prosthesis should occur, tear propagation throughout the device will usually result, causing joint failure.
The problem of tear propagation is particularly acute with patients suffering from severe rheumatoid arthritis. Rheumatoid arthritis produces alterations of the bone and tendon balance of the joint which play an important role in the mechanism of the reconstructed joint. Further, the bones of these patients typically become thin and atrophied and the edges of the bones at the joint may become very sharp. Subluxation of the joint bones results in impingement of the sharp bone edges on the midsection of the implant and subsequent lacerations or tears. Further, the implant itself may exert sufficient pressure on the bone to result in fracture of the bone.
The protective device disclosed in the aforementioned application Ser. No. 731,825, the disclosure of which is hereby incorporated by reference, is an elongated, one-piece sleeve which surrounds the stem portion of the implant and defines a passage for receipt of the stem portion. The protective device is surgically implanted within an intramedullary canal of the bone adjacent the joint. The protective end portion extends from the canal in a flared or fluted manner and prevents impingement of the edges of the resected bone on the flexible joint.